MANY WORKERS have repeated the observation by Aserinsky and Kleitman, in 1953,1of the cyclical recurrence of a physiologic state characterized by a low-voltage fast electroencephalogram (EEG), periodic bursts of rapid eye movements (REM), and a decrease in muscle activity.2Generally, there are four to five cycles per night and the predominance of slow-wave sleep in the first half of the night is followed by an increased incidence of REM periods during the last half of the night, in a pattern which is said to be fairly characteristic for a given individual.3,4The earlier studies of Dement and Kleitman,3as well as the more recent work of Williams et al,4have considered the REM cycle in relation to laboratory time, ie, time 0 is when the subject goes to bed and time is measured successively thereafter in terms of hours in the laboratory. The